Rubber compositions which contain particulate organic compounds are known. Patent Reference No. 1 describes technology in which reinforcing filler is partially replaced with organic compound particles—hollow particulate styrene-acryl-type cross-linked polymer or the like—for improved stiffness as well as reduced heat generation and wet road surface gripping characteristics. Patent Reference No. 2 describes technology in which a tire having a foam rubber layer which contains microparticle-containing organic particles fabricated as a result of physical mixture of microparticles and molten resin is employed to improve performance on ice, wear-resistance, and manufacturability at the factory.